In Uganda, HIV prevalence is estimated to be over 7% among those aged 15-49 and is rising. Yet, only 21% of Ugandans are aware of their HIV-serostatus. Community HIV testing has increased in Uganda and sub- Saharan Africa recently, and holds promise in efficiently reaching individuals from high-risk rural and migrant communities that are not touched by healthcare-based testing. In Uganda, most community testing is delivered in temporary, mobile venues, and can reach large numbers of people (up to 1,900 per day). Nevertheless, community testing presents considerable challenges for timely linkage to care after diagnosis. In rural settings, people who test positive may be referred to clinics many kilometers away; unpaved roads combined with lack of adequate transportation may deter care- seeking. Referral to care is especially difficult for high-risk migrant populations such as people in trading/market communities (who frequently move to different markets across the region), or fisherfolk (who spend most of the time fishing away from home, and who have multiple landing sites at different lakeshore locations). We propose to systematically explore barriers to and facilitators of linkage to care using iterative mixed (qualitative and quantitative methods, to ultimately develop novel solutions that are feasible for scale-up in diverse community testing venues. The specific aims are: (1) to use qualitative methods to understand the organizational protocol for, barriers to, and facilitators of linkage to care, and potential noel solutions, in three different types of community HIV testing settings (rural villages, trading communities, fishing communities); and (2) to examine quantitatively the barriers to and facilitators of linkage to care among people newly diagnosed with HIV at different community HIV testing settings. In Phase 1, we will conduct 10 qualitative interviews with key stakeholders in community-based organizations that conduct community testing, and observe three diverse testing scenarios in high-risk communities (trading communities, fishing communities, rural villages) to understand the current protocol for testing and referrals to care. We will also conduc qualitative interviews with 30 individuals who receive a positive test result to explore potential barriers to and facilitators of linkage to care. In Phase 2, we will quantitatively and longitudinaly examine barriers to and facilitators of linkage to care, as well as time to receipt of care, among sample of 240 individuals who test positive for HIV (80 per testing site type). In Phase 3, using an iterative process, we will conduct additional qualitative interviews with 5 key stakeholders (from Phase 1) and 18 HIV-positive testing clients (from Phase 2), in order to elicit feedback about the meaning of the Phase 1 and Phase 2 results, and input on innovative solutions for linkage to care following receipt of a positive test result in community HIV testing.